The prospect of a legal challenge in eurozone paymaster Germany is only adding to the jitters.

Mr Starbatty told the German Rheinische Post newspaper: ‘We will file a suit at the Constitutional Court against the credit from euro states.’

The paper said Starbatty and his colleagues viewed the aid package as an unlawful subsidy, because the loans were being offered to Greece at below-market interest rates.

The Maastricht Treaty contains a clause preventing EU states from taking on the debt obligations of their neighbours.

However, a court spokeswoman said no petition had yet been filed. And economists at Royal Bank of Scotland pointed out the same academics had twice before attempted to derail euro-initiatives.

In 1998 they sued the government over the introduction of the single currency, and in 2009 they attempted to block the EU’s Lisbon Treaty. In both cases the academics were unsuccessful.

In a research note, RBS analysts said: ‘We would be extremely surprised if Germany had not a priori investigated accurately whether the participation to the aid package is unconstitutional, and on balance we believe that the likelihood that a constitutional complaint could prevent Germany to disburse the cash is low.

‘However there are some small risks that a legal action against the government will slow Germany's ability to actively participate to the loan initially, we will continue monitoring the situation’.

He said: ‘A continuation of high public sector borrowing without the credible prospect of a return to sustainable public finances could have severe consequences for long-term interest rates, for economic growth, for the stability of the euro area and, therefore, not least for the monetary policy of the European Central Bank.’